1. Field of the Invention
The present invention relates to a zoom lens applicable to small apparatuses having an imaging function, such as a digital still camera, a mobile phone provided with a camera, and a personal digital assistant (PDA).
2. Description of the Related Art
In recent years, as the size of an imaging device, such as a CCD (charge coupled device) or a CMOS (complementary metal oxide semiconductor), in an imaging apparatus, such as a digital still camera, has been reduced, there is a demand for a small imaging apparatus. Therefore, in recent years, a technique has been developed which incorporates a so-called bending-type optical system that bends the optical path of a lens system into an imaging apparatus to reduce the size of the imaging apparatus in the thickness direction.
JP-A-2000-131610 discloses a zoom lens using a bending-type optical system that includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power arranged in this order from an object side, and moves the second negative lens group and the fourth positive lens group to vary power. In the zoom lens, a prism is provided in the first lens group to deflect the optical path at an angle of about 90°. In the first lens group, a fixed positive lens group is provided on the rear side of the prism. In addition, JP-A-2004-205796 (corresponding to U.S. Pat. No. 7,079,328) discloses a zoom lens that includes a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power arranged in this order from an object side, and moves the second positive lens group and the third negative lens group to vary power. In the zoom lens, a prism is arranged closest to the object side in the first lens group and deflects an optical path at an angle of about 90°. In the first lens group, a fixed lens group is provided on the rear side of the prism.
In the bending-type zoom lenses disclosed in JP-A-2000-131610 and JP-A-2004-205796, the fixed lens group is provided on the rear side of the prism for deflecting the optical path in the first lens group, and a zoom group is provided on the rear side of the fixed lens group. In particular, as disclosed in JP-A-2000-131610, in many cases, a positive lens group fixed during zooming is provided on the rear side of the prism for deflecting the optical path in the first lens group, and a zoom group is provided on the rear side of the fixed positive lens group. Further, in many cases, the zoom group includes a negative lens group and a positive lens group arranged in this order from the object side. However, in particular, when a bending-type zoom lens is used for a mobile phone, a lens module needs to have a small thickness and a small volume. However, the bending-type zoom lens according to the related art is designed to reduce a size in the diametric direction (a direction orthogonal to the optical axis after bending), but the length of the zoom lens in the optical axis direction after bending is not considered. This is because the bending of the optical path makes it possible to sufficiently reduce the size of the bending-type zoom lens. However, it is also important to reduce the total length of the zoom lens in order to reduce the overall volume thereof. Therefore, it is necessary to develop a bending-type zoom lens having a small total length.